M. I. H. (John Hornby Maw), ‘The Use of Indigo. Turner’s Drawings’, The Builder, vol.15, no.768 (24 October 1857), p.609
John Hornby Maw (1800–85), writing as ‘M. I. H.’, was the first to describe the deleterious effect of Girtin’s use of the fugitive indigo pigment and, more particularly, in the early watercolours of Joseph Mallord William Turner (1775–1851). Maw describes the effect of light on Turner’s Powis Castle (Manchester Art Gallery (1917.117)), but he might have equally been talking about one of the three watercolours by Girtin that he owned, the badly faded A Rainbow over the River Exe (TG1730).
In the days before cobalt and French blues were invented, water-colour painters had scarcely any alternative between indigo and Prussian blue. The use of indigo was, however, the rule, and that of the prussiate of iron the exception, because no pigment is so capable as indigo of representing aërial tints and tones, or so available in the formation of landscape greens and greys in every variety of tenderness or intensity.
This otherwise valuable pigment has, however, one fault of such magnitude as ought totally to exclude it from a place in the matériel of the conscientious artist. It is one of the most evanescent of pigments. I speak, of course, of the indigo of commerce, simply ground and made up for use as a water-colour … It is now some twelve years ago that an ardent admirer and collector of Turner’s water-colour works, on taking one of the England and Wales drawings out of the frame in which it had been exposed to the action of light for only a few months, was struck by the novel appearance of a clearly defined marginal band of colour, “fresher” or bluer than the rest, and extending all round the drawing. The fact was, the drawing had been put into a frame somewhat too small for it, and consequently a portion of the colouring had been covered by the "rebate,” and thereby protected from the bleaching power of light from which the rest of the drawing had evidently suffered. It was, however, equally evident that the component pigments had faded unequally, from the fact that the faded portion had become decidedly redder than the portion protected by the rebate. The pure bright yellows had gone but little, though perceptibly. The madder lake, as well as the ferruginous reds, remained in all their original power. The proprietor of the drawing to which I have referred decided at once upon what was afterwards proved to be the real cause of mischief, and was thereby enabled to understand how it was that he had so often been perplexed, in revisiting various collections of Turner drawings, by fresh discoveries of red clouds, &c. where he thought he used to see grey ones. An appeal was, however, made to Turner himself, who requested to see the drawing which it was alleged had faded. It was shown to him at his house in Queen Anne-street, in the presence of a gentleman well known to almost every collector of Turner drawings. On taking it into his hand Turner exclaimed, “I will never make another water-colour drawing,”–a resolution which he did not very long maintain. On being asked if he would have the kindness to blend the faded and unfaded portions of the damaged drawing a little, the answer was equally decided and characteristic. “Oh no! if I were to do that I should have all my drawings brought to be restored.” He admitted that he still adhered to the use of indigo, having supposed it to be a permanent material. On asking him whether he had not observed that all his early drawings, and those of Girtin, which had been long exposed to light, had become rusty, or what is called foxy, in colour, he made no answer, but said, “Well, what am I to use for greys?” The reply was, cobalt. I do not suppose that Turner used indigo from that time. By far the greater part of his drawings have been, however, made with this very fugitive pigment.
A Rainbow over the River Exe